This invention relates to primarily to an improved apparatus for digitizing of positions on a transparency, such as an X-ray or photographic film.
In various applications a digitizer can be utilized in conjunction with a light box to determine the positions of selected points on a transparency that is illuminated by the light box. For example, in one commonly used application, a light box is used to illuminate a transparency containing columns of DNA or RNA sequence information on X-ray film that is obtained from electrophoretic processing of proteins or other biological substances. A digitizer is positioned to have a working region (i.e., a region within which coordinate locations of selected points can be obtained, typically in digital form) over the illuminated surface of a light box on which the transparency is placed. An operator uses a stylus, or other marker of the digitizer equipment, to mark the location of points on the transparency, typically in a selected sequence. The coordinate locations of the marked points are determined by the digitizer equipment, and are usually stored under control of a digital computer or other electronic data processor.
A type of digitizer that is useful in applications like the one described is an acoustic digitizer of the type manufactured and sold by the assignee of the present patent application, Science Accessories Corporation, of Southport, Conn. an acoustic digitizer, acoustic wave pulses are typically emitted from the stylus of the digitizer equipment, travel through the air, and are detected at known locations. The transit time of the ultrasound energy in traveling from the stylus to the known locations can be utilized to compute the coordinates of the stylus location. Conversely, if desired, the acoustic waves can be generated at a known location or locations, and either be received by the stylus or bounced off a passive stylus or a finger to receivers, in order to determine the stylus location.
An advantage of the described type of digitizer is that it does not require wires or other opaque or semi-opaque media in the working region that could block light needed for the operator to clearly see what is to be marked. Also, there is no need to make contact with a surface below the item being digitized. Alternatively, sound transmission could be through a transparent solid medium, although this is considered less advantageous in that the medium would have to be positioned over the transparency.
Notwithstanding the stated advantage of utilizing an acoustic digitizer, an existing drawback is the temperature sensitivity of acoustic digitizer measurements, since coordinate locations are determined from transit times through media (typically air, but also possibly solid transparent media), and the speed of sound or ultrasound through such media varies substantially with temperature.
In applications where an acoustic digitizer is utilized for position determination on transparencies which are illuminated by a light box, the heat from the light box can cause inaccuracies and inconsistencies, and can contribute to user discomfort. Although techniques could be employed for electronically compensating for temperature variations in digitizer readings, such techniques can involve additional expense and/or complication of equipment, and may not provide complete solution to the problem.
It is among the objects of the present invention to provide solution to the described disadvantages in the prior art.